1. Field of the Invention
This invention relates to a method of multiplex transmission which is employed, for instance, in a vehicle, and more particularly to a method of multiplex transmission in which each multiplex node has its own node connection information and controls the node connection information for itself.
2. Description of the Prior Art
Recently increasing number of electronic instruments are mounted on a vehicle, which gives rise to a problem that the wiring between the instruments becomes too large and too complicated. In order to overcome such a problem, it has been proposed and put into practice to transmit signals between the instruments by multiplex transmission, that is, to connect multiplex nodes for the respective instruments to a common transmission path and transmit signals between the multiplex nodes by multiplex transmission. See, for instance, Japanese Unexamined Patent Publication No. 61(1986)-224634.
As a multiplex transmission system, there has been known a distributed control system, as a time division multiplex transmission system, in which each of the multiplex nodes controls its signal transmission and reception for itself independently from the other multiplex node. In such a distributed control system, there can be considered a system in which each multiplex node has its own node connection information for controlling its signal transmission and reception, and controls and corrects the node connection information for itself. The node connection information as used here means information on the condition of connection to the transmission path of each of the multiplex nodes which are connected to the transmission path to form a network, that is, on whether the communication system of each multiplex node is in normal state or in abnormal state.
In such a multiplex transmission, there arises trouble in multiplex transmission control of the overall network if there is an inconsistency between node connection informations of the multiplex nodes. Accordingly, when there is an inconsistency between node connection informations of the multiplex nodes, the node connection information must be corrected so that the node connection informations of the multiplex nodes are all equal to each other. Such a correction may be effected through a procedure in which, when one multiplex node realizes that another multiplex node which should be in abnormal state according to the node connection information of said one multiplex node should be in normal state according to the node connection informations of the other multiplex nodes, said one multiplex node transmits a request signal which requests to said another multiplex node to transmit a return-to-normal signal which represents that said another multiplex node has returned to normal and corrects its own node connection information when it receives the return-to-normal signal from said another multiplex node.
Further, the node connection informations of the respective multiplex nodes must be corrected each time the condition of connection changes. For this purpose, there can be considered a procedure in which, when one multiplex node which has been in abnormal state returns to normal, said one multiplex node transmits a return-to-normal signal, and the other multiplex nodes transmit, upon reception of the return-to-normal signal, request signals for requesting said one multiplex node to re-transmit the return-to-normal signal in order to check whether said one multiplex node has really returned to normal and correct their own node connection informations when said one multiplex node re-transmits the return-to-normal signal in response to the request signal.
However the former procedure gives rise to a problem that if one multiplex node transmits a node connection information and a plurality of multiplex nodes realize that a multiplex node which should be in abnormal state according to their own node connection informations should be in normal state according to the node connection informations of said one multiplex node and simultaneously transmit the return-to-normal signals, the traffic amount on the transmission path excessively increases, which can cause various problems.
Also in the latter procedure, there arises a problem that if one multiplex node returns to normal and transmits the return-to-normal signal, the other multiplex nodes can simultaneously transmit the request signals and the transmit amount can excessively increase.